Computing gun sight



May 31, 195 E. B. HAMMONDKJR COMPUTING GUN SIGHT 3Sheets-Sheet 1 Filed. May 17. 1947 \NVENTQR EDMUND B./7 /4MMOA/0,(/f.

7444, W ATTORNE y 1955 E. a. HAMMOND, JR 2,709,393

COMPUTING GUN SIGHT Filed May 17. 1947 :5 sheets-sheet 2 L/V TIME OF 51/6/47 GIj/V mun) "um"? INVENTOR a? Y W ATTORNE nite COMPUTKNG GUN sronr Edmund B. Hammond, Jr., Albertson, N. Y., assignor to The Sperry Corporation, a corporation of Delaware This invention relates to a computing gun sight and has 7 for its object the provision of a sight having a stabilized line of sight and an improved arrangement by which targets may be tracked with greater accuracy than has been possible with the well-known disturbed reticle sights. The latter sights control the line of sight definingsystem by the output of a lead angle computer which makes it difiicult, initially, to maintain the sight on the target. The sight line tracking error is usually magnified by the computing mechanism to produce a corresponding gun error of a larger magnitude.

The present invention provides a more stable line of sight by utilizing a system of the director type in which the line of sight is moved directly by control members, such as handle bars. The line of sight is moved in proportion to the displacement of the control members, and the associated computing mechanism ofiscts the guns with reference to the line of sight in accordance with the lead angle. Provision is made for preventing the line of sight from being affected by servo lag in connection with the operation of the turret, and therefore a target may-be tracked by the sight more easily than with former sights.

Another feature of the invention is the provision of a novel computing mechanism of simplified design which computes torques to be applied to the axis of a stabilizing gyroscope.

Still another feature of the invention is the provision of a computing sight having as a computing reference a I single gyro whose axis is always in the slant plane. With this arrangement there is no directional error due to lag in rate measurement, sometimes called roll about the gun barrel.

The sight of the present invention includes a gyro which stabilizes a gun turret, through the action of a turret servo system, against random motions of the structure supporting the turret. The gyro also provides an independent means for stabilizing an optical sight through the-action of stabilizing mirrors and difierential mechanisms. The gyro also is utilized to provide a means for controlling the angular rate of the sight line through the action of precessing springs in accordance with the ratio of lead angle to time of flight.

It will be understood that in order to accomplish these functions that the gyro is mounted in the sight with its spin axis parallel to the sight line, i. e., deflected from the gun line through an angle equal to the deflection angle.

In certain former gyro sights, hand control shafts are connected by means of the sight computing mechanism to the gyro processing springs. With this arrangement the hand control motion is essentially proportional to the angular rate of the gyro spin axis or sight line. The present invention provides a more accurate tracking arrangement by using a control system in which a small angular displacement is applied to the controlled sight line simultaneously with the application of the tracking rate, the displacement'and rate being introduced in a manner such as to cause sight line movements in the Zfldidii Patented May 31, 1855 same direction. This type of control system is known conventionally as an aided tracking system. In the present invention this type'of control is incorporated by causing reference pick-offs to move through an angle proportional to, but larger than the sight line of deflection angle, a value of 4/3 being arbitrarily selected for the constant of proportionality. Thus the line of sight is displaced from the gyro spin axis through a small angle, which in the case of the present invention is equal to (4/3d-A) or /3 A. Since the deflection angle A is proportional to the motion of the hand control, then the hand control can cause an immediate sight line displacement in addition to the rate which is generated through the action of the gyro processing springs.

In the sight of the present invention, the angular rate of the gyro spin axis is computed as the ratio of the lead angle to time of flight, and since the sight line and the spin axis are displaced from each other by one-third of the deflection angle, the rate computation is in error by one-third of the rate of change of the deflection angle. This error is generally quite small and has been ignored. Since the angular rate of the gyro spin axis is multiplied by time of flight to obtain the lead angle (reversing the direction of data flow), the gyro spin axis is sometimes referred to as the computing line.

With a single stabilizing gyro sight disclosed herein, it is possible to provide stabilization about all axes normal to the gyro spin axis, but not the spin axis itself. Angular error, however, about the spin axis may be observed through the optical system by the gunner who can correct for the same when carrying out his normal tracking procedure.

Other features of the invention will be found in the following description, given with the aid of the accompanying drawings, of which:

Fig. 1 is a schematic drawing of a gyroscope and a processing mechanism;

Fig. 2 is a schematic drawing of a mechanism for computing torques to be applied to respective axes of a y Fig. 3 is a schematic drawing of a mirror and difierential arrangement for stabilizing the line of sight against turret lag;

Fig. 4 is a detail drawing of a torque equalizing cam;

Fig. 5 is a diagram of the optical system; and

Fig. 6 is a diagram illustrating the operation of the sight.

The sight of the present invention is intended for use at will with either a radar sighting system or an optical sighting system. The present embodiment of the invention Will be described in connection with an optical sighting system and it will be understood that the operation thereof is substantially the same with either a radar or an optical line of sight. Furthermore, although the sight is discussed herein with reference to an airplane as the supporting vehicle, it will be understood that the improvements obtained by the present arrangement are equally advantageous in shipborne, land vehicle, and landbased installations. In addition, although the present embodiment of the invention is intended for local control in a gun turret, it will be apparent that the improved computing and tracking performance that is obtained may be applied as well to the control'of remotely located guns.

Referring now to Fig. i, the sight is provided with a hand control for target tracking purposes shown as handle bars 20, mounted on a horizontal shaft 21 supported for rotation in brackets 22 attached to a gear 23 which rotates about a vertical axis. A gear 24 fixed to shaft 21 meshes with a circular rack 25 fixed to shaft 26. This arrangement provides for the rotation of handle bars 20.

about two intersecting axes. When the handle bars are turned about their horizontal axis, shaft 26 is translated in a corresponding direction, and when the handle bars are rotated about their vertical axis, gear 23 is turned in a like direction. Gear 23 and shaft 26 are used to displace the line of sight in azimuth and elevation respectively, and in so doing cause respective mechanisms to precess a gyro and actuate the gun turret about corresponding axes as will be now described. The mechanisms for the respective axes are identical and, therefore, only that for the elevation axis will be described in detail.

A circular rack 3t) fixed on shaft 26 meshes with a pinion 31 fixed to shaft 32 which drives by means of gears 33 and 34 a shaft 35 fixed to a gear sector 36. The latter drives a gear 37 fixed to shaft 38 of a selsyn motor 40, having corresponding windings interconnected with a follow-up selsyn receiver 41. Another set of windings of selsyn receiver 41 controls the input circuit 42 of a total vertical deflection servo amplifier 43 whose ouput circuits 44 control total vertical deflection servomotor 45. A pinion 46 fixed to shaft 47 of servornotor drives a gear 50 which meshes with gear 51 on shaft 52 of selsyn receiver 41. This provides a follow-up arrangement by which any displaceernnt of handle bars 20 about their horizontal axis creates a signal at the input of amplifier 43 which in turn causes servomotor 45 to operate to such extent and in such direction as to displace the rotor of follow-up receiver 41 to wipe out the signal.

Any operation of servomotor 45 such as that just described also will cause corresponding movement of the line of sight and the gun turret. The mechanism for this purpose comprises a gear 55 which meshes with gear 50. Gear 55 is fixed to shaft 56 carrying gear 57 which drives a gear sector 60 supported for rotation about shaft 61 which is one of the horizontal shafts forming the axis of gimbal ring 62 of gyro '63. The gear ratio between handle bars 20 and gear sector 60 is such that the latter is displaced thereby in accordance with 4/3 total vertical deflection.

An E pick-off transformer 65 fixed to gear sector 60 cooperates with an armature 66 fixed to the horizontal shaft 61 0f the gyro. The E pick-off transformer and armature control over circuit 67 in the known manner an amplifier and servomotor, not shown, which position the gun turret in elevation. From the foregoing, it will be understood that any displacement of the control handles 20 effects a 4/3 displacement of the E pick-off transformer 65 which causes corresponding displacement of the turret.

The E transformers serve as signal generators for establishing voltage signals which are a measure of displacement between gyro and turret. Identical E transformers are provided for the lateral and elevation axes of the gyro. The lateral pick-otfestablishes voltage signals proportional to lateral rotation of the gyro gimbal relative to the E transformer field. The elevation pick-oif functions similarly with respect to rotations about the vertical deflection axis. The respective sector gears on which the E transformers are mounted are rotated according to the total deflection for that component but the resulting rotation of the E-shaped core is 4/3 total deflection for the component. Rotation of the E-shaped core with respect to the armature unbalances the secondary voltages. The magnitude of the resulting signal depends upon the amount of displacement between the armature and core; the phase of the signal depends upon the direction of displacement. The secondary voltages are fed to a conventional phase-sensitive demodulator and amplifier, not shown, for controlling the direction and rate of the turret. Through this control system, the guns are driven ahead of the gyro axis by 4/3 of the deflection angle, the gyro being driven at the tracking rate.

Control signals are also generated by the E transformer system when the airplane maneuvers. This provides a means for stabilizing the turret. Assume that the gyro is processing at a steady tracking rate and that the airplane deviates from its course of flight. Through the property of gyroscopic rigidity, the armature is held rigid by the gyro and does not move in the direction of deviation. However, the E-shaped core moves with the sight case, causing a displacement between the transformer and armature which induces a voltage signal. The turret then is driven in a direction opposite to the movement of the airplane, with the result that there is no apparent motion of the turret in space about the lateral and vertical axes of the gyro.

A precessing spring arrangement is provided for each of the azimuth and elevation axes, such as is disclosed in the application Serial No. 651,275, of Edmund B. Hammond, Jr., filed March 1,1946, now U. S. Patent No. 2,704,456. This mechanism, which is identical for both axes, will now be described in connection with the elevation axis.

As is Well-known, torque exerted about the elevation axis of a gyro causes precession about the azimuth axis, and torque exerted about the azimuth axis causes precession about the elevation axis. The spring arrangement about to be described is connected to the gyro at its elevation axis, and is used to precess the gyro in azimuth. Associated therewith is an arrangement for the purpose of preventing precessing springs from being actuated or stressed when the gyro turns about its elevation axis, for to do so would cause unwanted precession about the azimuth axis. The arrangement in one aspect is in the nature of a compensating differential which, generally speaking, winds or unwinds the torque spring in accordance with the displacement of the gyro about its elevation axis. A torque equalizer cam is also provided therewith which acts in opposition to the precessing spring to reduce the load on a rate drive mechanism, to be described.

Shaft 56 has a gear 76 fixed to its left-hand end which meshes with a gear sector 71 supported 'for rotation coaxially with the axis of gimbal ring 62 as defined by shafts 61. The gear sector 71 therefore will turn in fixed relation to gear 50 and control handles 20.

A pulley 72 is fixed to gear sector 71 in coaxial relation therewith. A stud 73, also fixed to gear sector 71, has upwardly extending arms 74 and 75 supported for rotation thereon. Referring to Fig. 4, these arms at their upper ends carry rollers which engage opposite sides of a cam 76 formed in one face of a pulley 77 mounted for rotation coaxially with respect to pulley 72. A compression spring 78 disposed between the arms presses the rollers thereon against opposite sides of the cam.

A shaft 80 supported for rotation in movable bracket 79 in parallel relationship with the axes of pulleys 72 and 77 has pulleys 81 and $2 fixed to the opposite ends thereof in register with pulleys 72 and 77, respectively. A band or belt 83 of flexible metal has one end attached to one side of pulley 82, the belt extending over the upper surface of pulleys 82 and 77, the opposite end of the belt being attached to the side of pulley 77 by a rivet, not shown. A similar belt 85 extending part way about and along the under surfaces of pulleys 81 and 72 connects these pulleys in the same manner.

A pair of oppositely wound processing springs and 91 are connected at one end to a hub 92 fixed to pulley 77. The opposite ends of these springs are connected to an arm 93 fixed to the gimbal ring 62. Springs 90 and 91 act as centralizing springs and when a torque is applied thereto by pulley 77, the springs communicate the torque to gimbal ring 62 and cause the gyro 63 to precess in the appropriate direction about its azimuth axis which is defined by shafts 94 fixed to opposite sides of the inner gimbal ring 95.

The torque applied to springs 90 and 91 is controlled by a rate computing mechanism, to be described, which causes the movement of bracket 79 back and forth with respect to the axes of pulleys 72 and 77 changing the distance therebetween in accordance with the computed rate, with the resulting Winding inone direction or the other of the precessing springs.

To reduce the loading on the computing mechanism the torque equalizer cam acts in opposition to the precessing springs 90 and 91. Output motion of the rate computing mechanism causes, as just stated, translation of bracket 79 and the idler pulleys 81 and 82, permitting pulley 77 to be rotated by the pressure of the rollers carried by arms 74 and 75 on cam 76 which causes the winding up of one of the precessing springs 90 or 91 depending on the direction of the rate. As the cam disc rotates proportionally to rate, the precessing spring exerts a torque tending to return the cam disc to the zero rate position. Without the torque equalizer cam,'the output of the rate computer would be acting against this total torque. However, the walls of the cam are designed so that, for any particular rotation of the disc, the rollers exert a torque which is opposite to the precessing torque. This torque has a magnitude such that a small constant and unidirectional residual torque is applied to the driving belts. In other words, the torque equalizer cam mechanism tends to rotate the disc away from the zero position, While the precessing spring tends to return the disc to zero position. As a result of this balance of torque, the force required to rotate the disc and wind up the precessing spring is only the residual torque which is necessary to maintain the proper band tension, neglecting friction in the bearings.

When the gyro is turned on its horizontal axis, as defined by Shafts 61, due to the operation of control handles or movement of the supporting aircraft, gear sector 71 is displaced accordingly, turning shaft 73 about the horizontal axis of gimbal shafts 61. The resulting displacement of arms '74 and 75 turns the cam 76 and pulley 77, thereby displacing hub 92 to which the precessing springs are attached in such direction as to compensate for the displacement of the gyro about its horizontal axis.

in addition to the various mechanisms described above, the control handles 2 directly operate, in the present embodiment of the invention, an optical sighting system. The optical system is shown schematically in Fig. 5 and partly shown in Fig. 1. Referring to Fig. l, a transparent mirror 1011 is supported for rotation about a horizontal axis by a pair of arms 1111 extending upwardly from a ring 102 which is rotatable in azimuth by -rneans of a gear sector 1113 fixed to the ring which meshes with a pinion 104 fixed to shaft 105. A gear 165 on shaft 1115 is driven from the azimuth gear sector 19?, which corresponds to the elevation gear sector ih'in accordance with total lateral deflection. The azimuth gear sector is displaced by control handles 2%) when rotated about their vertical axis by an arrangement similar to that already described for the elevation axis which comprises gear 23 attached to the control handles which drives gear 119 on shaft 111. Shaft 111 carries a gear 112 which drives gears 113 and 114, the latter being fixed to the shaft of selsyn motor 115 which controls follow up selsyn 116, amplifier 117 and servomotor 113 in the manner already described.

Servomotor 118 drives sector 1177 through appropriate shafts and gears 119, 120, 121, 122 and 123 according to 4/3 of the total lateral deflection angle. The gear ratio, however, for actuating the mirror 1% about its azimuth axis is such that the mirror is deflected according to total lateral deflection.

Mirror 1110 is turned by the control handles 20 about its horizontal axis as defined by shaft 125 according to total vertical deflection by means of a gear 126 which couples gear sector 6t? with a gear sector 127 fixed to shaft 128. An arm 129 fixed to shaft 128 actuates a vertical rod 139 which deflects a plate 131 along which the end of a second vertical rod 132 may slide as the mirror 1110 is turned in azimuth. Rod 132 engages an arm 133 fixed to horizontal shaft on which the mirror 1% is mounted and thereby deflects the-mirror'in. elevation directly in accordance with the movements of control handles 20.

A linkage mechanism shown in. Fig. 2 is used to compute torques to be applied to the respective axes of the gyro. Certain ballistic cams and a time of flight shaft are shown in Fig. 2 in connection with the linkage mechanism which are parts of a ballistic computer of the kind disclosed in application of Edward J. Nagy and Edmund B. Hammond, Jr., Serial No. 563,068, filed November ll, 1944, now U. S. Patent No. 2,579,510.

The linkage mechanisms for the lateral and elevation axes are substantially the same, so only that for the elevation axis will be described in detail.

Both linkages are controlled from a common time of flight shaft which is displaced by a ballistic mechanism, not shown in accordance with the logarithm of a suitable function of time of flight.

Shaft 140 drives shaft 141 through gears 142.. A time cam 143 is fixed to shaft 141. Cam 143 has aspiral groove formed in its surface.

A collar 145 provided with pin 146 which rides in cain groove 144 is free to turn on the cam. A gear 147 formed on a portion of the collar is in mesh with an elongated gear sector 148 which is actuated, as will be explained, by a shaft 149 in accordance with a gimbal correction function. it will be understood that relative movements of shafts 141 and 149, due to the action of cam groove 144 will cause collar 145 to translate in one direction or the other along the cam. This movement is used to translate a fulcrum 150 for a lever 151, the fulcrum being connected with collar 145 by means of a forked member 152 which'rides in a groove formed in the collar. A guide rod 15 which extends through an opening in the forked member 152 is used to guide the fulcrum as it is translated.

Lever 151 has one arm pivoted by pivot to a yoke 151. The opposite end of lever 151 translates a shaft 162 according to vertical rate, as will be explained. Shaft 162 engages bracket 79, Fig. l, and translates the vertical rate idler pulleys 81 and 82 which, as already explained, impart a corresponding torque through the precession springs 99 and 91 associated therewith to the arm Hi9 fixed to the inner gimbal ring 95 thereby causing the gyro to precess about its elevation axis shafts 61.

Anotherlever 1&5 forming part of the torque computing system is actuated by a lift pin 166 of a cam 167 of the ballistic system in accordance with the elevation ballistic deflection. This cam, which is part of the ballistics system disclosed in the above-mentioned application is rotated by gear 168 in accordance with gun elevation. One end of lever is actuated according to total vertical deflection by a shaft 170 coupled with a rack 171 and driven from gear sector 60 via gear. 172, shaft 173 and gears 17 i and 175, rack 171 being in mesh with the latter gear. The opposite-end 176 of.lever 1t55 engages a roller 177 in yoke 161.

Referring to Fig. 1, gear 174 has a linkage connected off center thereto consisting of pivotally connected links 18% and 181 the latter being fixed to shaft 149 of the gear sector 148 which is operated by the linkage in accordance with a gimbal correction which is the logarithm of a suitable function of 4/3 total vertical deflection.

A similar arrangement actuated by ballistic earn 183 is provided for computing lateral rates.

Gravity correction is provided by a spring 184 attached to the lateral stabilization mirror shown in Fig.5. This spring is stretched in accordance wtih the gun elevation angle by a cam in the ballistic system, not shown.

In operation, the translation of rack 171 is'fed to the linkage 165'. The fulcrum of lever 165 is positioned by the vertical windage deflection output from cam 167 in the ballistic unit. The output of the linkage (TVD-VWD) represents vertical prediction plus gravity correction and is fed to the time of flight linkage lever 151. The movable fulcrum for this lever is translated according to the motion of the time cam collar 145, or, in other words, time of flight with gimbal correction. The linkage acts as a dividing linkage, the output being TVDVWD or vertical rate plus gravity rate. This rate is fed by shaft 162 to the pulley differential as already described. As the idler pulleys 81 and 82 are translated proportionally to rate, the bands wind or unwind on one of the second pair of associated pulleys causing pulley 76 to rotate. Rotation of this pulley imparts a torque to arm 109 of the gimbal ring 95 as already described. As the torque is applied about a vertical axis the gyro processes about its horizontal axis at a rate and in a direction dependent upon the vertical rate output of the linkage. This precession of the gyro displaces the vertical pick-off armature 66 with respect to the E transformer 65, since the armature is attached to the outer gimbal 62 which moves in response to the vertical motion of the gyro. The resulting voltage signal causes the guns to be driven in elevation at a rate, and in a direction controlled by the output of the linkage divider.

As previously explained, the output of the time of flight linkage is a translation proportional to the torque required to precess the gyro at target rate plus gravity rate torque. Target rate is the ratio of predicition to time of flight. However, the torque applied to the gyro cannot be made proportional to this angular tracking rate. This is the case because the gyro is displaced from the gun line and, hence, the torque vector is not always perpendicular to the gyro axis. Referring to Figure 6 which is a diagram showing the relative positions of the gun line and gyro axis with reference to the gimbal axis MN, the precessing torque is applied to the gimbal about the axis MN perpendicular to the guns. The precessing torque is equal to the product of the applied force at B and the constant radius B. The force is the ratio of the applied torque to the variable distance 0A. This distance is maximum when there is zero displacement between gyro axis and gun line. As the gyro axis is displaced from the gun line, the length of the moment arm 0A decreases and hence,

without gimbal correction, the applied torque for any particular tracking rate would increase accordingly, thus causing false rates to be introduced into the mechanism. T o avoid this condition, a correction which depends on this angular displacement must be made to the applied torque. This correction, which can be plotted approximately as a cosine curve, is called the gimbal correction.

The preceding explanation refers only to gimbal correction for displacement of the gyro in one plane. Since the gyro is displaced about its lateral and vertical deflection axes, each gimbal must be corrected for both lateral and vertical displacement of the gyro. The gimbal correction function that is used is the best average function that could be obtained, taking into consideration simultaneous displacements in both components, without involving mechanisms of undue complexity.

'The gimbal correction is introduced into the sight by modifying the time-of-flight input to the linkage multiplier so that the output rotation is the gyro rate corrected for gimbal action. Thus,

I 1 Vertical rate= flw Vertical rate where and s ')=1og (T)-log 14/3 TVD) As shown in Fig. 2, the fulcrum of the multiplier is positioned by a collar riding on a groove cam. Rotation of the cam causes translation of the collar and with it the fulcrum. Likewise, rotation of the collar according to the output of the log f(4/ 3 T VD) linkage causes translation of the fulcrum. Thus, the groove cam acts as a differential that subtracts the logarithms of time-of-flight and the gimbal correction function. The collar also positions the fulcrum of the multiplier linkage so that the output of the linkage is the ratio of the linkage input (prediction=TVDVWD) and corrected time-of-flight. This ratio is proportional to the vertical precessing torque which appears as a rotation of the hub of the vertical precessing spring' in the same way, the lateral precessing torque includes correction for gyro displacement.

The optical system includes a vertical stabilization mirror and a lateral stabilization mirror 191 which serve to prevent the line of sight from being affected by turret lag about either the elevation or lateral axes. This stabilization arrangement is fully described in the application Serial No. 656,379 of Edmund B. Hammond, Jr., filed March 22, 1946, and therefore will only be briefly described here.

The optical system shown in Fig. 5 includes the conventional light bulb 192, a stadiometric reticle 193, a mirror 194 which reflects the image of the reticle to lateral stabilizing mirror 191, from which it is reflected to vertical stabilizing mirror 190 and thence through a suitable collimating lens 195 to the transparent mirror 100.

The stabilization mirrors 190 and 191 are free to rotate through small angles about their axes under control of individual differential pulley systems.

Referring to Fig. 3, the differential pulley arrangement for controlling the vertical stabilization mirror consists of a pulley 196 fixed to the outer gimbal ring 62 and a corresponding pulley 197 fixed to the axis of gear sector 60. These pulleys cooperate with pulleys 198 and 199 supported at opposite ends of bar 200 fixed to shaft 201 on which mirror 190 is fixed for rotation. A spring loaded belt 202 of thin wire is Wound about the pulleys as shown in the drawing, the belt being secured at one point, not shown, to pulley 196 from whence it is led over the tops of pulleys 196 and 193, underneath pulley 197, over pulley 199, and then back to pulley 197. Loading spring 293 couples the ends of the belt.

When there is a displacement between E transformer 65 and its armature 66, which displacement represents turret lag, a rotation of the pulleys results, causing a deflection of the vertical stabilization mirror and the line of. sight. This deflection depends on the amount and direction of the displacement and thus the line of sight is corrected for turret lag. When the E transformer and armature are again aligned, the stabilization mirror is re turned to the zero correction position.

Operation Assume a condition where the gyro, armature and E transformer, line of sight and hand controls are aligned at a zero reference position. When the hand grips are displaced vertically, for example, the elevation E transformer is displaced with respect to the sight case (i. e., gun line) by 4/3 TVD. The gyro tends to maintain its spin axis (the reference axis) directionally fixed in space and, hence, there is displacement between the vertical E transformer and its armature. Through electrical connection to the turret servo mechanism, not shown, the turret is driven in elevation in the direction of hand grip displacement. However, as the hand grips are displaced, a precessing torque proportional to the vertical tracking rate is applied about the inner gimbal of the gyro, thus causing the gyro to precess vertically at a tracking rate, the magnitude and direction of which are established by maintaining the line of sight on the target. Hence, by the energization of circuit 67, the turret, and with it the guns and sight, move about the vertical deflection axis of the gyro until there is zero displace ment between armature and transformer. As a result, the guns lead the gyro axis vertically by 4/3 TVD.

Since the transparent mirror 100 is geared to the hand controls, the line of sight is deflected vertically by TVD in response to the vertical motion of the hand grips. Therefore, the guns lead the line of sight by TVD, and the line of sight leads the gyro axis by TVD Furthermore the line of sight is displaced instantaneously in the direction of precession of the gyro, thus improving the tracking operation. This desirable condition is accomplished by using a response factor greater than unit, i. e., 4 3.

Assuming the target is flying along a straight line, and since the line of sight lies in the plane of the gyro axis and gun line, and moves in the same direction as the gyro spin axis, it tends to move off the target at the initial tracking stage. As the operator continuously adjusts the hand grips to hold the line of sight on the target, torques are applied to the gyro to precess it in the direction of target travel. Hence the velocity direction of the gyro axis, line of sight and gun line are moved continually in the direction of target travel. Successively smaller increments of correction are required in the position of the hand grips to precess the gyro so that the spin axis is finally moving in the direction of target travel. When this condition obtains, the line of sight remains on the target and the gun line leads the gyro by 4/3 total deflection and also leads the line of sight by the total lead angle. Thus a series of approximations of the total lead angle have been made until, at the instant when the gyro moves in the direction of the target and the line of sight is on target, the correct lead is set in. This lead, therefore is proportional to hand grip displacement.

What is claimed is:

1. In a lead angle computer, a lever having a fulcrum, means for displacing the fulcrum in accordance with windage deflection, control means coupled with one end of the lever for displacing the same in accordance with a total deflection angle, a second lever having one end controlled by the first mentioned lever, a fulcrum for the second lever, means for displacing the fulcrum of the second lever in accordance with time of flight and gyro precessing spring means actuated by the second lever.

2. In a lead angle computer, a lever having a fulcrum, ballistic cam means for displacing the fulcrum in accordance with a ballistic deflection angle, hand control means coupled with one end of the lever for displacing the same in accordance with a total deflection angle, a second lever having one end operativelyengaged by the opposite end of the first lever, a fulcrum for the second lever, means for displacing the latter fulcrum in accordance with time of flight and gyro precessing springs controlled by the opposite end of the second lever.

3. In a lead angle computer, a lever having a fulcrum, means for displacing the fulcrum in accordance with windage deflection, control means operatively coupled with one end of the lever for displacing the same in accordance with a total deflection angle, a second lever having one end controlled by the first mentioned lever, a fulcrum for the second lever, means for displacing the latter fulcrum in accordance with time of flight, gyro precessing springs, and means controlled by the second lever for actuating the gyro precessing springs.

4. In a lead angle computer, a lever having a fulcrum, cam means for displacing the fulcrum in accordance with windage deflection, manually operable control means operatively coupled with one end of the lever for displacing the same in accordance with a total deflection angle, a second lever having one end operatively coupled to the first mentioned lever, a fulcrum for the second lever, differential means for displacing the latter fulcrum, means for operating one input of the differential means according to time of flight function, means for operating a second input for the differential from the control means to correct the time of flight function in accordance with the angular position of the control means, and gyro precessing spring means controlled by the second lever.

5. In a lead angle computer, a lever having a fulcrum, ballistic cam means for displacing the fulcrum in accordance with ballistic windage correction, hand control means coupled with one end of the lever for displacing the same in accordance with a total deflection angle, a second lever having one end operatively connected with the opposite end of the first lever, a fulcrum for the second lever, means for moving the fulcrum of the latter lever comprising a spiral cam, means for turning the cam in accordance with a function of time of flight, gyro precessing springs, and means controlled by the opposite end of the second lever to actuate the gyro precessing springs.

6. In a lead angle computer, a lever having a fulcrum, ballistic cam means for displacing the fulcrum in accordance with ballistic windage correction, hand control means coupled with one end of the lever for displacing the same in accordance with a total deflection angle, a second lever having one end operatively connected with the opposite end of the first lever, a fulcrum for the second lever, means for moving the fulcrum of the latter lever comprising a spiral cam, a collar thereon having a pin cam follower fixed thereto, means for turning the cam in accord ance with a function of time of flight, means for turning the collar operated by the hand control means to correct the time of flight function for the instantaneous position of the hand control means, and a member operatively connecting the collar with the fulcrum of the second lever, gyro precessing springs, and means controlled by the opposite end of the second lever for actuating said springs.

References Cited in the file of this patent UNITED STATES PATENTS 

